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Posted: 8/6/2010 10:53:43 AM EDT
| If I put a colt lower receiver on my BCM Mid lenght upper with 16" barrel, will the rate of fire change any on full auto from the normal carbine length gas system with 14.5" barrel it is normaly attached to? |
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Normally I would say that there shouldn't be any real measurable rate of fire change between a 14.5" upper and a 16" upper as you are effectively only changing the gas dwell time (the time the bullet remains in the barrel once it passes the gas port by 1.5 inches)
However, the reality is that there are more than just gas dwell time associated with ROF. One of the key factors is going to be the gas port size. Generally speaking a 14.5" barrel should have almost the same size gas port at a 16" gun so all you have really changed is the dwell time of 1.5 inches of additional barrel length. However, since they are two separate uppers they could have different gas port sizes, different chamber dimentions, slight variation in how the gas block is alligned with the hole in the barrel or the gas key is installed on the carrier all of which affect ROF. The number of rounds down the barrel (older/more used uppers seem to speed up to some extent as gas rings wear and any rough/friction spots in the receiver wear, the bolt cam pin also becomes more polished, as well as the actual 90 degree bends in the gas system start to round over smoothing the gas flow or the gas port starts to erode and open up. These factors are sometimes tempered by the gas tube or gas block starting to foul over time depending upon the previous cleaning regime, so you really never know how all these combination of factors are going to play out. I would suspect that if they were both uppers from the same manufacturer and of the vintage and rounds down the tube you would probably see less than a 100 RPM change between the two, with the 16 inch being theoretically faster due to the increased dwell time and identical gas port sizes, resulting in more gas pushed back down the tube and cycling the action faster. Just my guess. James Austin, Texas |
| Yeah it might slow down a tad since the mid-length gas tube is a little longer taking slightly more time to unlock the bolt. However really for more dramatic RPM changes you should play with buffer weights. Like if i put a standard carbine buffer in my M-16 the RPM's are very fast, but then if i swap it out for a heavy 9mm buffer it slows way down. |
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